Mercado was born on June 6, 1951, in Caloocan. He studied at St. Joseph School and completed his philosophical and theological formation at the Jesuit-run San Jose Seminary. After becoming a priest, he took his licentiate in theology at the Angelicum in Rome (1981–1984).
He was ordained to the priesthood on March 19, 1977, for the Archdiocese of Manila. There, he served as assistant parish priest of San Isidro Labrador Parish in Pasay (1977), spiritual director at the San Pablo Regional Seminary (1977–1979), director of the Pre-College Department of the San Carlos Seminary (1979–1981), professor of theology at the San Carlos Seminary (1985–1988), rector of the Holy Apostles Seminary (1988–1994), and rector of the Pontificio Collegio Filippino (1994–1997).
He was named titular bishop of Talaptula and auxiliary bishop of Manila on February 25, 1997, and was ordained on March 31 of the same year.[1]
He was appointed as the first bishop of the Diocese of Parañaque on 7 December 2002 and formally installed on 28 January 2003.
